


What Goes Unwritten

by volatileSoloist



Category: Gravity Falls, Slender (Video Game)
Genre: A gratuitous crossover fic, I spent a year making this potato salad, Minor Injuries, Mystery Twin Antics, Post-Canon, References to Marble Hornets, Spooky, Started writing this when Indred Cold was introduced in TAZ so I borrowed him, They're teens now so they curse!, a year!
Language: English
Status: Completed
Published: 2019-08-16
Updated: 2019-08-16
Packaged: 2020-09-01 22:04:49
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 8,484
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20265241
Author URL: https://archiveofourown.org/users/volatileSoloist/pseuds/volatileSoloist
Summary: For my best friend in the whole world. It took a year, so I promise you don't owe me the twenty bucks anymore <3Dipper and Mabel Pines return to their second home, Gravity Falls, two summers after Weirdmaggedon. A lot has changed, and much has stayed the same: before long, they find themselves embroiled in a mystery revolving around an elusive cryptid that even Ford can't track down.





	What Goes Unwritten

The slow screeching of a rundown bus’ breaks had never brought Mabel as much joy as it did today. Sure, she’d gotten used to a similar sound on her way to school, but _this_ was a _particular_ rundown bus: the 1044 Speedy Beaver, the only public transportation that made regular trips into Gravity Falls.

They were finally back again. Mabel and Dipper, the Mystery Twins, returning to the scene of their best and _wildest_ summer ever! It felt like forever since Mabel had seen that seemingly innocent stretch of woods along the highway, but she knew by now that these woods were _far_ from innocent. No, they held some of the biggest mysteries and wackiest creatures in the world!

As the bus rumbled to a stop, Mabel could’ve sworn she saw the light from the headlights reflecting off a pair of large, probably gnomish, eyes, before they blinked and vanished into the depths of the brush.

Mabel turned to her brother, Dipper. “Bro-bro, did you see—”

“Already on it!” Dipper replied, and true to his word, he was scribbling away in his favorite notebook. It was kind of like a surrogate for Ford’s journals: even though Bill had destroyed them two summers ago, Dipper would still reflexively reach for them anytime he saw something interesting.

So Mabel had suggested he make his own. Their therapist had seconded the motion, pointing out that journaling was a good coping mechanism for anxiety, which Dipper had in spades after Weirdmageddon. With a little decorating help from her, Dipper’s journal was ready for action; it became just as useful and well-used as Grunkle Ford’s, even if the things Dipper was writing were pretty mundane.

But they wouldn’t be mundane for long. Not if Gravity Falls had anything to say about it!

And it was ready for them, too. No more than a few minutes had passed since Dipper and Mabel disembarked the bus, before a familiar red El Diablo pulled up to the edge of the forest with a squeal. It was an impressive sound, but it wasn’t as great as the squeal Mabel let out when the car doors opened, revealing an ecstatic Grunkle Stan, and a queasy-looking yet still excited Grunkle Ford.

“Kids!” yelled Grunkle Stan, running towards his great-niece and nephew.

“Grunkle Stan!” cried Dipper and Mabel, running towards their first grunkle and crashing into him with gusto. Their combined momentum canceled out, and they toppled to the ground, hugging tightly all the way.

“Ugh,” groaned Grunkle Stan, “I think you broke something.”

“Really?” Mabel asked, eyes wide with concern.

“Yeah,” he grouched. “Ya broke my heart! It’s been too long, kids, been too long.”

“It’s not our fault!” Dipper responded indignantly. “You were still off on your boat trip last summer!”

“Aw, you big softy,” Mabel gushed, hugging Grunkle Stan all the tighter in light of Dipper’s accusations.

“What?! Me, a _softy?!_ You’re gonna ruin my tough reputation!”

The three of them were still hugging and laughing as Grunkle Ford approached. “Good to see you, kids! How have you been doing in sch—” He didn’t have time to finish as Grunkle Stan extended an arm, grabbed his brother, and pulled him down into the Hug Pile.

“Alright, alright,” Grunkle Ford chuckled. “I missed you kids, too.”

They sat and hugged a few moments longer, until from within the bushes, they heard a small voice say, “You guys having a moment here, or something?”

With that, the pile unraveled, all heads turning to look at the woods, where two small, bearded figures were poking their heads out from behind the bushes.

“Gnomes!” Mabel said, pointing a finger. “I knew it!” She paused for a moment, and then added, “Man, you guys are smaller than I remember.”

“Rude!” the first gnome scowled. “You’re less shiny than I remember.”

“Oh, yeah!” Mabel beamed, and she gave them a wide, straight-toothed grin. “Buh-bye braces!”

“Schmebulock,” said the other gnome, nodding approvingly.

“Hey, gnomes!” Grunkle Stan finally cut in. “Quit being so nosy, ya little twerps.”

The first gnome gasped in offense. “I’ll have you know that a big nose is a point of pride among gnomes!”

“What_ever_,” Grunkle Stan said dismissively; simultaneously, Grunkle Ford exclaimed, “Fascinating!”

There was the sound of scribbling, and Mabel turned her head to see her second Grunkle rapidly scrawling in… a journal?

“Ohmygosh!” Dipper exclaimed. “You have a new journal?”

“What?” Grunkle Ford asked, sounding distracted; when Grunkle Stan elbowed him, he perked up and turned to Dipper. “Yes, as a matter of fact! Ever since Bill destroyed my old ones, and I started my new adventures with Stanley, I’ve been trying to both catch up to where I was before, and record anything new I learned while I was abroad.”

Dipper was practically bouncing up and down. “Can I read it? Please, Grunkle Ford?”

“Of course!” Grunkle Ford smiled. “I’m sure you have a better memory than me these days; you might be able to help me rewrite some of the old entries!”

“Thank you thank you thank you!” Dipper said, hands already reaching out to receive Journal 4.

“Schmebulock,” Schmebulock interrupted.

The first gnome nodded. “Yeah, you guys are kinda on my front lawn.”

“Fine, fine,” Grunkle Stan said, standing up and dusting himself off. “You nerds can talk back at the Mystery Shack. Besides, I told Soos we’d be picking you kids up, and I’m sure he’s dying to see the two of you!”

Mabel grinned, jumping to her feet. “C’mon, Dip-Dop, we can’t leave Soos waiting!”

“Right,” Dipper said, and he got up, hesitatingly followed by Grunkle Ford. He suddenly brought a hand up to the worn brown hat on his head, and he asked, “Does Wendy still work at the Mystery Shack?”

“Nah,” Grunkle Stan huffed. “Soos offered to hire her, but she ended up getting some fancy lumber-gig a ways north of here.”

“Oh,” Dipper said, looking crestfallen.

“She does still visit from time to time, though,” Grunkle Ford added. “Charming girl. Lots of chutzpah.”

“Yup, that’s Wendy,” Dipper said with a small smile.

“Oh my god,” Mabel laughed, and she pushed Dipper toward the Stanmobile. “If you quit fantasizing, you might actually get the chance to see her!”

“O-of course!” Her twin acquiesced, and the two hopped into the back seats of the car and buckled up, followed shortly by their two grunkles.

“Perhaps we should drive a little more safely, Stanley, now that we’ve got the kids in tow?” Grunkle Ford said sternly as Grunkle Stan revved the engine.

“Ha!” Grunkle Stan laughed, “I wouldn’t worry, Poindexter. These kids can handle it.”

With that, the car did a sharp U-turn, and sped back along the road into Gravity Falls.

——

In short order, the twins were set up in the attic of the Mystery Shack. They had a wonderful time saying hello to Soos, and seeing all the new attractions that he had set up. In much the same fashion as Grunkle Stan once had, he had cooked up an incredible taxidermy chupacabra, complete with a wolf head, a pair of sabre cat teeth, and the body of a chimp.

They’d also said hello to his girlfriend, Melody. Mabel knew back when she and Soos first met that they’d be perfect together, and lo and behold, she was right! They were still as close as ever. She’d really gotten into the whole charade of the Mystery Shack, having leveled up from basic cashier to business partner while the twins were gone, and she sported a suit, eyepatch, and fez to match Soos’.

Dipper was disappointed to see that Wendy was _not_ in fact waiting for them at the Mystery Shack. She had, however, left both him and Mabel small wooden carvings of their iconic symbols, the pine tree and shooting star. Receiving his little totem seemed to satisfy Dipper for the time being.

The house was essentially the same way they left it. Same cozy living room, same creaky but comforting attic, same decrepit kitchen. Or at least, so they thought.

After a nice ‘welcome back’ dinner amongst their family and friends, Grunkle Ford ushered Dipper and Mabel to the vending machine, Grunkle Stan following shortly behind. He punched in the secret code for the elevator, and the group of four entered to begin the descent into the basement.

“What’s going on, Grunkles o’ mine?” Mabel asked, leaning against the side of the elevator.

“Did you detect some kind of new anomaly?” Dipper questioned, looking equal parts excited and anxious.

“Nah,” said Grunkle Stan dismissively, “your Grunkle Ford just wants to show of his fancy new set-up, and _I’m_ going to bed.”

Before either of the twins could inquire further, the elevator settled to the final stop, and the doors slid open.

Both of their jaws dropped.

The basement had been completely redone. Where there once had been a spacious lab, there was now a narrow, wood-paneled corridor, with a shut door on either side and one open at the end of the hall. Through that final door, they could see the blinking lights and cables they’d come to associate with this floor of the Mystery Shack.

“Wow,” Mabel said, moving down the hallway. “It’s a lot _smaller_ down here than I remember.”

“It’s kind of claustrophobic, actually,” Dipper added, looking slightly uncomfortable.

Both of the twins moved to the doors on the opposite sides of the hallway. As their hands landed on the brass doorknobs to investigate, two wrinkly old grunkle hands pressed against those doors, keeping them shut.

“There’s not much of interest in there, I’m afraid,” Grunkle Ford said, giving them a small apologetic smile.

“It’s where we live now,” Grunkle Stan explained. “Casa de Stans, now that Soos, his grandma, and his girlfriend are all staying upstairs, at any rate. Now, you kids go ahead and check out the lab that my brother is absolutely dying to show you. I’m hittin’ the sack.”

The kids bid their first grunkle farewell, and when Grunkle Stan closed his door behind him, Grunkle Ford practically bounced ahead, with an excited, “C’mon, kids! Come see!”

Mabel and Dipper shuffled down the corridor, both eager to see what their more sciency grunkle had been working on as of late. Indeed, as they entered the lab, they took note of all the many beeps and buzzings that rang throughout the spacious former portal room.

“So...” Dipper began as he wandered up to one of the larger machines, “_Did_ you detect a new anomaly?”

“No, no, nothing like that,” Grunkle Ford waved off, “Things have been relatively calm since Weirdmaggeddon ended. Most of the effects of Bill’s chaotic magic have long since dissipated.”

“Most, but?” Mabel pressed, curious at the open-ended statement.

Grunkle Ford paused for a brief moment, before turning away from the twins and heading to a desk pressed up against one of the walls. He rifled in the drawers for a moment before pulling out a medium-sized red book.

Dipper’s eyes widened. “Another journal?” he practically squealed, bouncing up and down.

“Oho, more than just one, Dipper!” And with that, Grunkle Ford pulled out several more from the drawer.

“Ohmygod,” Dipper said, looking like he might pass out. “How much did you learn while you were gone?”

“Well,” Grunkle Ford hesitated. “Not all of it is new information; some of these are journals that I’m using to re-enter old information. Since Bill destroyed my old ones and whatnot.” He stopped for a moment, and glanced at Dipper, who had stopped bouncing around, and instead had begun to look somewhat guilty.

Noting the disheartened look on Dipper’s face, Grunkle Ford crouched down to his level. “Don’t worry, Dipper. Once I was compromised, it was almost guaranteed that Bill would find them. I don’t blame you.”

Dipper looked away. “Are you sure? Believe me, I’d under—”

“Not a single iota,” their grunkle said firmly, before standing up. “Nothing I’d recorded in them was unique among the phenomena located in Gravity Falls, anyway. Since I’ve returned, I’ve already gotten about a third of my old data re-recorded. You see—”

“You see, Dipper?” Mabel whispered, “You don’t have to worry about that anymore. Just like Dr. Indred said.”

“I know,” her brother mumbled. “But I can’t help it. I feel like I let him down.”

“He just said you didn’t, ya ding-dong.” Then she softened. “It’s okay now.”

“Thanks, Mabel,” Dipper acquiesced with a small smile.

The siblings tuned back in to Grunkle Ford’s monologue. “—of course, my memory isn’t perfect, so I’ve had to do some field research, but all in all, I’d say my efforts have been successful.”

He dropped several of the journals back in the desk drawer before handing one of them back to Dipper, who resumed looking like he was about to faint as he took the book with reverence.

“This,” Grunkle Ford said with an air of hushed excitement, “is what you’re looking for. All my discoveries of new creatures and phenomena around the globe are recorded in this journal.”

“Thank you!” Dipper whispered, and then without further ado, he all but ripped open the book, eyes quickly scanning the first page.

He was brought out of his reverie when Mabel elbowed him. “Gonna let me look too?”

“Oh,” Dipper said, looking sheepish, “Of course!”

Grunkle Ford smiled fondly at the two of them. “You two feel free to look it over while I get some work done. Let me know what you think!” He then plopped down into his desk chair, pulled it in, and took out another journal.

“See Dipper,” Mabel whispered again, “Grunkle Ford ‘craves validation’ just like you!”

“Pshhh!” Dipper said, a flush creeping up on his cheeks. “You can’t quote Dr. Indred to me, Mabel.”

“Can too.”

“Mabel,” Dipper sighed, “do you want to read Ford’s fascinating new journal with me or not? ‘Cuz the suspense is kinda getting to me!”

“Haha, okay bro-bro,” Mabel relented. “Let’s pop it open!”

With that, the twins sat down on a nearby bench and opened the book once more. On the first page of the book was a slightly waterlogged drawing of a large, tentacled creature labeled ‘The Nordic Kraken’.

_Specimen was encountered off the shores of Malmö, Denmark. Weather turned from clear skies to churning and stormy within the span of ten minutes. Five minutes later the fascinating beast, as tall as our boat is long, emerged from the waters and latched onto our vessel. Specimen was a dark slate grey as opposed to the red of a giant squid. Storm powers?_

__

__

_Weaknesses: Harpoons, Stanley’s fists._

“Whoa,” Mabel said, letting out a hushed gasp. “I always thought those things were myths!”

“I guess there’s more weirdness hotspots in the world than just in Gravity Falls,” Dipper said with a shrug. Then he sighed dreamily. “I wonder what it was like to actually be there and see it.”

“Probably bonkers, considering they had to fight it off!” Mabel said, pointing to the ‘weaknesses’ section. “Haha, ‘Stanley’s fists’. Can you believe Grunkle Stan punched a giant squid? No, wait, I can totally believe that.”

“Yeah,” Dipper grinned, and he turned the page. Staring back at him were several detailed drawings of a scary-looking creature, with the body of a goat, giant bat wings, and a deer skull for a head. “Oh, I know this one! It’s a Jersey Devil.”

_We went ashore briefly to visit our hometown of Glass Shore Beach. What was supposed to be a weekend trip turned into a several week-long detour as one day, my weirdometer picked up strong readings in the woods across the highway leading out of the city. We set up watch, and later in the evening, a whole herd of Jersey Devils emerged at the edge of the trees. When they retreated, we pursued, and we got to glimpse their activity for an entire evening._

_Despite allegations of human attacks, Jersey Devils seem to be docile creatures when unprovoked, and the specimens spent their time grazing in a moonlit clearing. In a later encounter, I discovered that their fearsome appearance is a ruse in order to deter predators. Whatever creatures were bold enough to attack in spite of that (i.e. wolves) received quick retaliation from the herd with their sharp horns and hooves in order to protect their young._

“Ford’s writing has gotten a lot more prose-like,” Dipper commented absently.

Mabel pounded her palm with her fist, “He’s going soft.”

“Mabel,” Dipper laughed, “It’s not a bad thing. It just reminds me of _my_ journals,” he added shyly.

Mabel gazed raptly over her brother’s shoulder as they read the next few pages, ooh-ing and ahh-ing at the various fantastic beasts. They flipped a page, and suddenly, Dipper let out an astonished gasp. “I’ve—I’ve seen this one before, here in Gravity Falls!” He sounded almost ill.

“Jeez,” Mabel winced, staring at the image of a brain with a floating pair of eyes and mouth, surrounded by a tangle of veins. “I don’t remember this one at all. Do you think I blocked it out?”

“No,” Dipper said, shaking his head. “You were too hopped up on Smile Dip.”

“Oh yeah,” Mabel said, “Haha.”

Dipper briefly scanned the entry before flipping the page. “It’s more creatures from Gravity Falls. Ford must have encountered these ones for the first time after coming back from his trip.” Dipper turned another page, before frowning and flipping back to the brain. Then he pointed to the center crease of the book. “A page’s been ripped out here.”

“You’re right,” Mabel said, and she leafed back to where they had been before and added, “One’s missing from here, too.”

Together, the twins perused the last pages of the book, noting where sheaves of paper had been torn from the binding. “That’s like... eight missing pages?” Dipper said, counting on his fingers. “Ford doesn’t make mistakes like that.”

“I mean,” Mabel shrugged, “he probably does, but I’m still pretty intrigued by this. Wanna go ask him about it?”

“Uh, heck yeah?” Dipper said, before slipping a loose scrap of paper in to mark his page.

“Grunkle Ford!” The twins called out, walking back to the desk.

“Yes? Got any questions about my work?” Grunkle Ford asked, gazing eagerly at the two teens as he rubbed his hands together.

“Yeah,” Dipper said, before placing the journal next to Ford, opening it, and showcasing the torn page edges. “What’s up with these missing pages?”

Immediately, Grunkle Ford paled, and the change was so sudden that Dipper faltered in his accusatory expression, shifting instead to one of confusion.

“What’s wrong, Grunkle Ford?” Mabel asked, placing a sweater-covered hand on his sleeve.

“It’s—it’s nothing, Mabel,” their grunkle said, pulling at his turtleneck, “I just made some mistakes and ripped out the pages.”

Mabel turned to Dipper with a ‘told you so’ look on her face. Dipper, however, shook his head stubbornly. “I don’t believe that. You’re too meticulous! And when you _do_ make mistakes, you just cross stuff out.”

“Well,” Grunkle Ford faltered, before shaking his head and saying, “It’s nothing you need to worry about.”

“Uh, that _always_ means that it’s something to worry about,” Mabel said, crossing her arms.

“Just tell us! We’re older now, we can handle whatever you’re keeping from us!” Dipper said, using his best adult-convincing voice.

Finally, Grunkle Ford caved. “Fine, just... don’t tell your Grunkle Stan about this, okay? I don’t want him to be worried about it.”

Mabel and Dipper’s eyes grew large. “Why would he be worried?” Dipper asked, while Mabel simultaneously assured, “You can count on us!”

Grunkle Ford hesitated, pausing for a moment before finally turning to his desk and pulling a false bottom out of his lowest drawer, revealing multiple crinkled pieces of paper. Wordlessly, he picked them up and handed the pile to Dipper.

What Dipper saw on the pages both disturbed and completely baffled him. They weren’t fully coherent entries like Grunkle Ford normally wrote. They seemed to be scribbled hastily in charcoal, and each had an ominous warning on it in big block letters.

**FOLLOWS — CAN’T RUN — HELP ME — DON’T LOOK... OR IT TAKES YOU — ALWAYS WATCHES, NO EYES — LEAVE ME ALONE — NO NO NO NO NO NO...**

Periodically, there would be pages with drawings of a tall, slim figure wearing a suit.

“Creepy,” Mabel said with a shiver.

“I...” Dipper murmured, “don’t really know what to make of this.”

“It’s alright, I can... sort of explain,” Grunkle Ford said, scratching his head. “I started making trips out into the woods late at night, hoping to catch a glimpse of the floating eyeballs I’d first noted in Journal 3. When I finally did, the specimen retreated further into the woods. I followed it, only to quickly become hopelessly lost in a part of the forest I had somehow never explored before.

“Immediately, I felt like I was being followed. I felt a prickling on the back of my neck as if someone was watching me. Yet the woods were deadly quiet. Then, I began to hear a soft sound, coming from nearby.”

Grunkle Ford paused, and he looked away, appearing chagrined. “Unfortunately, I was never able to ascertain _what_ the sound was, because the next thing I knew, I was lying on the ground outside of the woods, and it was morning. I had a big headache, a hole in my memory, and one of these pages that you’re holding.”

“Wow,” Dipper said softly, mouth agape.

“_Creepy,_” Mabel repeated, her interest piqued.

“I tried to return to this section of the forest seven more times, and each attempt ended the exact same way. That’s around the time I gave up. I had no memory of even writing those pages, so I tried to dismiss them as nothing, and I ripped them out of the journal.”

“Is it another demon from the Mindscape?” Mabel asked. Out of the corner of her eye, she saw Dipper tense, but she plowed forward nonetheless. “Maybe something that escaped after Weirdmaggeddon?”

“No, that’s impossible,” Grunkle Ford stated firmly. “I’m positive that everything that crawled out of the Mindscape was sucked back in when we closed the rift.”

“Then that means it’s something new!” Dipper crowed, and he jittered up and down in excitement. “Grunkle Ford, can we help you look for it?”

“Absolutely not!” Ford said immediately, and Mabel winced at the resulting heartbroken look on Dipper’s face. “Whatever that creature is, it has danger written all over it. Look, if Bill couldn’t get into my mind, but this creature _can_, what does that say about its level of power?” He shuddered, and shook his head. “I don’t want you looking for it.”

Mabel shot a knowing glance at Dipper, and Ford coughed pointedly. “With _or_ without me. I know kids your age like to get up to all sorts of hijinks unsupervised, and just because you’re older doesn’t mean that you’re wiser, or more careful.”

“But Ford—” Dipper argued, but quieted as Mabel laid a hand on his arm.

“It’s fine, bro-bro. Maybe Grunkle Ford is right.”

Dipper looked shocked. “Mabel, since when do _you_ listen to Grunkle Ford?”

“It’s the, uh, maturity! We’re teenagers, so we listen to adults!” Mabel replied with a laugh. She took Dipper’s hand and began to determinedly tug him in the direction of the elevator. “Night-night Grunkle Ford!”

“Mabel!” Dipper said, resisting until Mabel covertly reached over and pinched his side. He almost yelped, but he bit it back, giving Mabel a curious look.

Ford, on the other hand, seemed bemused. “You’re going to bed already?”

Mabel glanced back at him and gave him a friendly wave, replying, “We’ve had a long day of traveling, ya know? Dipper and I need a lil’ bit of rest and relaxation before the _real_ adventures begin!”

Ford rubbed the back of his head in confusion, but acquiesced. “You’re right. A proper sleep schedule is very important! I’ll be up for a while though, so free to come back down if you want to read any of the other journals!”

“Will do!” Dipper agreed, and with that, Mabel pulled Dipper into the elevator and pressed the button for the ground floor.

——

“Mabel,” Dipper hissed, “How can we just give up on something like that?” It wasn’t like his twin to just listen to authority. That would be acting too much like _him_.

“Shh, you dum-dum!” Mabel glanced around the elevator, looking for something that wasn’t there. She leaned in, and in a hushed tone, she told him, “Of _course_ we’re going to go looking for it, Dipper!”

“Really?” Dipper said, once again surprised by Mabel.

“Duh! It’s freaky for _sure_, but I know that you wouldn’t want to miss out on it! And I’m not gonna let you do it alone. Mystery Twins forever!”

Dipper smiled gratefully at her, and then pounded his palm with his fist. “_Especially_ if it _is_ something from the Nightmare Realm.” 

Mabel nodded her agreement. “But we gotta be sneaky about it, or else Ford and Stan will try and stop us.”

Dipper sized Mabel up. She seemed serious about this, which was both great _and_ uncharacteristic of her. Slowly, he asked, “You’re not just agreeing to this because you fe—”

“No!” Mabel interrupted, almost vehemently.

The elevator dinged, and both twins were startled enough to jump back with a yelp. As the door slid open, Mabel let out a sigh and said, “Listen, I just think it’s a cool monster! It ain’t got _nothing_ to do with any feelings I may or may not have about what happened two summers ago, so don’t go all psychologist-mode on me!”

Dipper raised both hands up in a placatory manner. “Ok, ok, I get it.” He and Mabel stepped out of the archway, and the door shut behind them before the vending machine swung back into place. “So,” he said, “We’ll start tonight, under the cover of darkness!”

Mabel nodded, her trademark grin appearing once more. “We’re gonna get to the bottom of this! No monster’s too difficult or sneaky for the Mystery Twins!”

——

It seemed that the monster _might_ have been too sneaky for them.

Dipper and Mabel began to set up a series of night watches over the next week or so, wandering around the forest looking for the patch of woods Ford had mentioned. They looked all over, even asking some of the other forest creatures to help, showing them the lost pages of Ford’s journal (Mabel had pilfered them a day or two after they found out). All of them swore up and down that they didn’t know what they were talking about, which Dipper found extremely frustrating.

“I’m running out of ideas,” Dipper sighed one night as he climbed down from their watch-tree. It was a little past midnight, and he yawned. He flicked on his flashlight and stared absentmindedly into the circle of light it projected. “Yeah, we could just stumble around the woods for the rest of the summer, but I think we’re going to need to gather some solid clues, or evidence, or _something_ in order to find this thing.”

Mabel jumped down after him and scratched her head, thinking hard. “I mean, we could try going to Gnasty’s and asking around?”

“Gnasty’s?” Dipper responded, perplexed.

“The gnome tavern,” Mabel clarified. “I went there once with the girls to figure out how to get the unicorn hair for the Mystery Shack.”

“Oh yeah,” Dipper exclaimed, but then paused, “Wait, didn’t you get someone in there arrested? They might not want to see you again.”

Mabel frowned. “I mean, I guess? But it’s been two years, so they might not remember!”

Dipper nodded, “Sounds like the best bet to me.”

“They won’t help you,” a voice hissed from behind them.

Dipper and Mabel jumped at the sound and immediately whirled around, aiming the flashlight into the darkness, but there was nothing there.

“Who was that?” Dipper asked, raising a hand defensively. “Show yourself!”

From behind them, again, “I will not.”

The twins turned again, as fast as they could, but there was nothing that Dipper could see. Suddenly, a memory surfaced in the back of his mind, and Dipper said, “Back to back, Mabel!”

The twins spun around to cover both directions, and briefly, ever so briefly, Dipper caught the glow of yellow eyes at the edge of his flashlight, before there was a rustle of foliage and the eyes disappeared. Suddenly, from the tree above them, there came a slight rattling sound.

“Oh my god,” Dipper breathed out, “You’re the Hide-Behind!”

The rattling noise intensified. “A crude name.”

“What’s your name, then?” Mabel asked, not moving from her position. Dipper cautiously glanced out of the corner of his eye at the tree, but could see nothing from his side.

A slightly different rattling noise came from the tree, sounding like a mixture of branches shifting and soft chittering. There was a pause, and then the Hide-Behind said, “That is my name.”

“I... don’t think I can pronounce that?” Dipper said, bemused.

Mabel laughed from behind him. “Don’t worry, Dipper, I got you covered.” There was a clicking noise, and then, there—slightly tinny-sounding but unmistakable—was the rattling noise. “I brought a recorder!” she exclaimed, sounding proud of herself.

Dipper was impressed too. Evidently, so was the Hide-Behind, because it murmured, “Clever human.” It went silent again, before whispering, “The place you seek does not exist, because it is not a location bound to this plane of existence. It roves with the being you desire to know of.”

Dipper began to feverishly scrawl in the journal. “How can we find it, then?” he asked distractedly, as he finished writing, “POCKET DIMENSION?”

The Hide-Behind laughed softly, a sound like the scraping fingernails of against tree bark. “You may not like what you find. You are dangerously close to the threshold at which it will not tolerate humans in its domain.”

Dipper quirked an eyebrow. “What do you mean by that?”

“You will find out,” it said ominously. “If you follow me, I will lead you to where you may be able to find it.”

“It’s getting late,” Mabel protested, before clicking the recording and broadcasting the creature’s name back to it. She yawned as she said, “I’m not used to staying up this late.”

“Maybe you’re not,” Dipper rebutted, before adding, “We might not get another chance at this!”

“You will not,” the Hide-Behind confirmed. “I am only risking my hide for you now because you had the decency to learn my name.”

“Fine, fine,” Mabel said, rubbing her eyes before quickly shaking her head back and forth to wake herself up. “So how are we supposed to follow you when we can’t see you?”

The Hide-Behind laughed again, but this time, the sound came from a bush a little ways away. “Follow my call.”

——

Mabel and Dipper rushed along the forest floor, pushing aside branches and bushes as they chased the sound of the Hide-Behind, which was ahead of them by several yards. Every time they got stuck on something, its next call would sound farther and farther away.

Each bit of forest they ran through seemed identical to the last, and yet for the most part, it wasn’t unfamiliar. Mabel was fairly certain they had already searched some of these areas before. Was the Hide-Behind leading them in circles?

As they entered a denser patch of brush and undergrowth, it became increasingly hard to keep up with the creature. He quickly outpaced Mabel, as her sweater kept getting caught on low-hanging branches, until Dipper was ahead of her by several feet. “Dipper, wait up!” she yelled.

He only glanced back briefly, with a hurried, “C’mon Mabel, it’s gonna be too far away soon.” He paused before shouting, “Slow down!” to the Hide-Behind.

“Dip-Dop,” Mabel panted from behind him, out of breath from running so far, “if I go any faster, I’m gonna—_whoa!_” Suddenly, Mabel yelped as her ankle caught an exposed and gnarled tree root, and she pitched forward to the forest floor with a resounding thud. “Owwww, crap.”

“Mabel!” Dipper yelled, and he turned around to jog back to her. “Are you okay?” he asked, hands hovering over her as though unsure of where to start.

She sat up with a pained hiss. “I think I might have twisted my ankle,” she bemoaned, and as he took inventory of her health, she added, “I’m also pretty scraped up too.”

“Hang on,” Dipper said, shrugging off his backpack to dig inside it. “I think I have some first aid supplies in here—” 

“Dipper,” Mabel whispered suddenly, glancing around in confusion. “I don’t think I bumped my head _that_ hard, but I don’t recognize this bit of the forest at all!”

Her brother glanced up, and his hands stilled as he looked at the trees surrounding them. The trees were packed even more densely than before, a cold mist hovering low to the ground around them. “Yeah,” he said slowly, “This doesn’t even look like where we were just now.”

Mabel grabbed the flashlight from Dipper and scanned the ground with its beam. “I can’t even see the root I tripped over. What the hell?”

Dipper jolted suddenly. “Oh crap, wait, where’s the Hi—I mean, where did they go?”

“Dunno, Dipper... we might have lost them?” She turned up the volume on the recorder before playing it, as though shouting the Hide-Behind’s name. “Where did you go?” she called.

The Hide-Behind didn’t respond. What _did_ answer them was a low buzzing sound, almost like TV static. It didn’t seem to be coming from any specific direction, but rather it was all around them. Just a soft, creepy humming that never stopped.

Dipper straightened up in alarm before holding a hand out to Mabel. She grabbed it and let herself be hauled up, wincing slightly as she accidentally put weight on her injured ankle.

“We need to move,” Mabel said in a hushed but urgent tone. “I don’t like this place, it’s got bad juju, Dipper.” She leaned on Dipper’s shoulder, and he put his arm around her back to keep her stable. Mabel handed him the flashlight.

“Yeah,” Dipper said, glancing around nervously. “It’s definitely not making things any easier on my paranoia.” He peered into what little of the gloom the flashlight illuminated, and was just barely able to make out a stretch of dirt, forming a road deeper into the forest. “Look, there’s a path! Maybe it’ll help us get out of the woods.”

“I hope so,” Mabel said fervently; together, they walked further into the trees, brushing aside low hanging branches and listening for sounds other than the crunching of their feet on dry foliage, the occasional crickets, and the ever-present humming. “I never knew the woods in Gravity Falls could feel so... _unwelcoming_.”

Dipper shuddered. “I don’t think we’re in Gravity Falls anymore, Mabel.”

“Haha, nice reference Dip-Dop.”

_Deflecting her anxiety with humor, as usual_, Dipper thought, rolling his eyes as he continued to move at the slow pace Mabel needed in order to hobble along.

Eventually, out of the darkness, a tall red structure began to loom, high enough that Dipper couldn’t see all the way to the top. It was cylindrical, and as Dipper slowly paced around it, he could see that there was an opening in the back, like there had once been a door that rotted away over time.

“What the heck is this?” Mabel asked, head turned skyward to the open roof.

“If I’m correct, I think it’s a si—”

“Waitwaitwait, Dipper, you could totally climb to the top of this!” Mabel interrupted. “You could get up there using the pieces of wood like a ladder, and you could maybe see a way out of the forest!”

Dipper looked up where Mabel was focusing, and indeed, slats of wood and fallen timbers made almost a ladder up to the very top of the silo. He hummed indecisively. “I dunno Mabel, I don’t want to just leave you down here, cuz you can’t climb up.”

“I’ll be fine Dipper,” Mabel said, brushing him off with a roguish wink. “I’ll shout if I need you.”

Dipper scratched the back of his head awkwardly, glancing once more before sighing. “Yeah, sure. Just keep a close eye out for anything strange, okay?”

Mabel nodded, grinned, and gave a thumbs up. “You got it, bro-bro. I’m the ghoul guard!”

With that, Dipper held the flashlight in his mouth and began to climb. The boards were slightly damp, and flaked a bit under his touch as he climbed, giving him small splinters in his fingers to curse over. He almost lost his balance once when a board buckled beneath him as he stepped on it, but he quickly recovered his footing and made his way to the top.

Dark and misty forest stretched out before him for what seemed like miles and miles. The trees rustled lightly in a chilled wind, but there was no light anywhere to be seen. What he could see, however, was what looked to be a large roof looming in the center of the forest. “Mabel, there’s a building out there we could probably hide out in,” Dipper called down.

He was just about to start clambering down when he saw the figure standing across from the base of the silo.

Dipper couldn’t make it out very well, but it looked to be pale, and wearing dark clothing. Immediately, he was shaken with an overwhelming sense of unease, vision blurring slightly as he tried to focus in on it.

“Nope,” he muttered, and began climbing down as fast as possible. “Nope nope nope nope nope.” He jumped the last few feet, bracing his landing with a hand to the ground before rushing to Mabel and helping her into a standing position. “Okay, we’re gonna go _as fast as we can_, Mabel.”

Fortunately, Mabel only nodded with wide eyes instead of arguing, and leaning against him, she hobbled along at his side. Dipper resolutely did not turn around to look behind him, but the prickling feeling on the back of his neck got stronger and stronger. Mabel, however, had no such reservations apparently, and she turned her head and yelped. “D-Dipper, there’s something following us...”

“I know,” Dipper said through gritted teeth. “We’re gonna keep moving. I have a plan to lose it!”

Slowly, slowly, the two shuffled along the trail, Dipper half-carrying Mabel in order to keep up a decent pace. And still, the buzzing, staticky noise grew louder and louder as they moved. Mabel was huffing and puffing with the strain, with Dipper not faring much better either, but finally the building he’d seen before came into view. He wasn’t sure what it was, exactly, but he knew what he needed to do.

He came right to the side of it, and he placed a knee on the ground and held his hands out, cupped together. “I’m gonna boost you up, Mabel. He might not be able to get us on the roof!”

“I don’t know if I can,” Mabel said, but nonetheless she hobbled forward, and bracing herself against the wall, she placed her good foot in Dipper’s grip, and as he let out a deep breath, he pushed upward with all his might.

Mabel jumped with the movement, letting out a hiss of pain as she scrabbled at the edge of the roof. “I—I can’t—” she cried out despairingly, before apparently mustering all of her strength and clutching hard onto the edge, shimmying her way to the top of the roof. Without so much as a pause for breath, she turned around, held out her hand, and said, “Okay, jump, Dipper!”

But Dipper could hear the static, already so loud. The monster was too close, he could feel its eyeless gaze fixed on him... he knew he wouldn’t have time. And so, fists clenched, he turned and began to run in the other direction. “I’m gonna draw it away Mabel! Stay safe up there, and I’ll be back!”

“Dipper!” Mabel protested, but he had no time to wait. He ran, feet pounding hard against the soil, until he was almost to the edge of the clearing.

He was just about to disappear into the trees when he heard Mabel let out a bloodcurdling scream.

——

Mabel scooted to the center of the roof as she observed her brother running. _Dipper is such an idiot. A brave idiot,_ she conceded, _but an idiot all the same._ Mabel knew with absolute certainty that he wouldn’t be able to outrun the monster. Neither of them would. All they could hope would be for the sky to lighten with dawn. _If this dimension even has a dawn._

She was watching Dipper make his way to the treeline when she felt it, that telltale static cling sensation all over her skin. Slowly, she turned her head, and when she saw that faceless white head peeking over the edge of the roof, and slowly _rising_ as it climbed up to meet her, she let out a horrified scream.

It clambered over the edge, limbs bent unnaturally as it rose from all fours to a standing position. Her vision started blurring intensely, and her head felt stuffed full of cotton, but this close, she could see that the monster indeed had pale white skin, and was dressed in a dark black suit. Stretching out from its back were several wriggling limbs, tentacle-like in nature.

“No no no no!” Mabel yelled, trying her best to crawl away, but she didn’t get far when a cold hand grabbed her by the scruff of her sweater and lifted her up. She kicked her legs out wildly, hoping to kick it and get it to let her go, but it was no use. It turned her around so that she was facing it, and at this point, there was so much magical interference that she could hardly even see. Her struggling began to weaken, and despite being the optimistic twin she thought, just for a second, that this might actually be the end.

Then something touched her forehead, and her vision magically cleared. She blinked her eyes several times, and saw that the monster was still holding her, but it had touched one of its tentacles to the top of her face.

Her head felt echo-ey for a moment, and then she heard a voice inside it, quiet but raspy.

It said, _Who did this to you, child?_

Mabel blinked again, this time out of confusion. Still shaking with fear, she thought, _What? Who did what?_

With its free hand, the monster gently tapped Mabel’s injured ankle. She winced for a moment, but then realized what the monster was asking. _No one did this... I—I was clumsy and tripped over a tree root._

_You need not lie to me, child._

_But I’m not,_ Mabel protested, _My brother Dipper could tell you that!_ Speaking of which, where _was_ Dipper anyway?

“Let her go, you monster!” Dipper cried, huffing and puffing as he shakily and clumsily pulled himself over the edge of the roof. He charged at the creature, flashlight raised like a weapon as he rushed forward.

“Dipper, wait!” Mabel cried, and he all but screeched to a halt. Just as quickly, the monster stretched out an arm and scooped Dipper up too. He struggled just as hard as she had, when the monster touched his forehead too. _Speak, child,_ Mabel heard it say, _Your sister claims the injury she sustained was an accident, and not caused by harm from something more... sinister._

Dipper’s mouth agape, he remained quiet until Mabel pinched him. _It was an accident. We were running around looking for you when she tripped._

The being cocked its head to the side, and was silent for a moment before it communicated again. _That is a shame. I would not have wanted children to be harmed because of me._

_What do you mean?_ Mabel asked. _And we’re not children, we’re teenagers!_ She added huffily.

At that, the monster let out a creaking laugh, like a squeaky door being swung on its hinges. _You are a child, young one._

Pushing past the condescension, Dipper frustratedly interjected, _I don’t understand how you’re friendly. Grunkle Ford seemed _terrified_ of you._

_I channel a specific kind of energy to keep adult humans away from me,_ the creature explained patiently.

Mabel raised an eyebrow. _Why?_

Once again, the monster paused. Then it sighed and began, _It is my sworn duty to protect the children of your realm, when they have been harmed by those who by all means ought to have been nurturing them. Parents, guardians, or perhaps even strangers. I ward off all of these people so that I may extract the child and bring them to safety, before exacting penance on those humans... the _real_ monsters._

“Wow,” Dipper said out loud, genuinely perplexed. Then he added, _But I find it really hard to believe that any of the adults in Gravity Falls would hurt their kids. They’re too nice!_

_Some monsters hide in plain sight,_ the creature intoned ominously.

_Wait, then why were you attacking Grunkle Ford? He loves us, he’d never ever hurt us!_ Mabel objected. This whole experience was boggling her mind so much that the fear was rapidly fading away.

The monster nodded its head. _While that may be true, if word ever got out that there was a child-stealing monster in the woods, the townspeople would burn it down looking for me. They would never find me, but the forest would suffer immensely. And so I have been capturing your ‘Grunkle Ford’ each time he has come looking for me, and been wiping his memories in order to preserve it. Then I return him home. No harm done, and no one is the wiser._

At that remark, Mabel and Dipper turned to each other, exchanging a nervous glance. _Um, well, you see,_ Dipper began hesitantly, _Grunkle Ford took notes of his encounters with you._ He reached into his backpack and pulled out the pages that Ford had hurriedly scribbled on in a panicked scrawl.

The monster twitched, and then was totally still. _May I have them._

_I mean,_ Dipper hemmed and hawed, _He’s gonna wonder where they went._

_Please give them to me. You will make up a story about losing them in the woods. Humans are good at lying._ The monster deposited them on the ground and held out one now-free hand for the papers. _No one can know. Please._

Dipper bit his lip nervously. _Well..._

“Oh my god, Dipper,” Mabel said, her heart aching with sympathy for this creature, before continuing, “Just give him the papers. Grunkle Ford didn’t want to keep investigating this anyway.”

Dipper sighed. “Fine.” He held out the papers, and Mabel watched as the monster took them, folded them carefully, and put them in a pocket.

_Thank you, young ones. I will return you to your world, now._ The monster went to remove their tentacles.

_Wait,_ Mabel asked suddenly, _Can we at least know your name?_

The monster hesitated, but then nodded. Even without facial features, Mabel could tell it was smiling when it rasped, _I am Slenderman. Goodbye, children._ It moved closer and placed its cold hands over their eyes.

And then Mabel and Dipper were suddenly at the edge of the forest, sitting on the ground and watching as the sun rose over the Mystery Shack.

“Well that was an adventure,” Mabel said, breaking the silence, and she grinned when Dipper couldn’t help but laugh.

“That’s putting it mildly!” Dipper agreed, and he helped Mabel to her feet. Her ankle still hurt, but at least they were out of the woods.

They were only a few feet from the door when it suddenly flew open, and both grunkles came storming out to meet them.

“What were you doing out there all night, you little troublemakers?” Grunkle Stan scolded, looking the kids over and immediately honing in how Mabel was leaning on Dipper for support. “And what happened to _you?_”

Grunkle Ford looked even more concerned than his brother. “Do you realize how dangerous what you did was? There’s a monster on the loose!”

“We were fine,” Mabel said—not technically lying—with a smile. “I just tripped over a root while we were trekkin’ around.” When neither grunkle looked satisfied, she added, “We’ll be more careful next time!”

“You better,” Grunkle Stan huffed, “Or your parents would never let us hear the end of it!” Seemingly satisfied, however, he turned and headed back toward the shack. “I’ll make some breakfast, you two must be starving after running around the woods all night.”

“‘Kay!” Dipper and Mabel yelled back.

Once Grunkle Stan was inside, however, Grunkle Ford squatted down next to them and looked at them sternly. “I _did_ tell you not to go looking, you two. What you did was very dangerous. That being said, well,” and his expression changed to one of eagerness, “did you find anything out? I’m on the edge of my seat here!”

Dipper winced, and he rubbed the back of his head as he said, “Not a single clue, Grunkle Ford. We looked all night and covered the whole forest, but we couldn’t find anything. It was a total bust.”

“And Dipper lost your papers,” Mabel added in, tone cheeky, “So that didn’t help.”

Grunkle Ford looked aghast. “You _lost_ them? Those were the only clues we had!”

“I’m sorry, Ford,” Dipper said, staring resolutely down at his feet. “We both went tumbling, and I almost lost my backpack. When I found it, half of my stuff was gone, including the papers.”

Grunkle Ford looked disappointed, but then he sighed. “It’s okay, Dipper. It seemed like a dead-end anyway. And anyway,” he added, more brightly this time, “I’m just glad that you two are okay!” He looked at Mabel, faltered, and said, “Well, mostly okay. Why don’t we get you inside and I’ll see what I can do about helping with your ankle.”

“Thanks, Grunkle Ford, that’d be great!” Mabel replied, and Grunkle Ford stood, nodded, and began to trek back to the Mystery Shack, gesturing over his shoulder for them to follow.

Dipper and Mabel did _not_ follow, however. Not yet. They glanced back toward the forest. This had been one of their wildest nights in a long time, by far. The spent a moment to let out a breath of tension, and inhale the cool pine breeze.

Then, and only then they turned, heading back to the comfort of the Mystery Shack. The excitement may have been over for now, but with Gravity Falls being—well—_Gravity Falls_, they knew the summer could only get even wilder from here on out.

And better yet, they knew they were ready.

**Author's Note:**

> It was nice to return to writing Gravity Falls stuff, but damn if this wasn't a tough fic to write.
> 
> Also, this post is where I got my headcanons for how Slenderman behaves, if it seemed familiar to you: https://halosblogthing.tumblr.com/post/44270210669/blackfoxnightmare-uninhibitedandunrepentant


End file.
